1. Field of the Invention
The present invention relates to switching controllers, and more particularly to a switching controller of parallel power supplies.
2. Description of the Related Art
In order to fulfill the high-speed need for computer and communication systems, a power supply is required to deliver more current to CPU and its peripherals. However, such a high current demand increases power losses in the power supply. The power loss of the power supply is proportional to the square of its switching current.PLOSS=I2×R  (1)
where I is the switching current of the power supply, and R is the impedance of the switching devices such as the resistance of the inductor and the transistor, or the like.
Higher output current results in lower efficiency and the efficiency is more adversely affected for the power supply with low output voltage. In recent development, parallel-output technologies have been developed to solve this problem. Examples are, for instance, “DC-to-DC controller having a multi-phase synchronous buck regulator”, U.S. Pat. No. 6,262,566 to Dinh; “Multi-phase converter with balanced currents” by Walters et al., U.S. Pat. No. 6,278,263; “Multi-phase switching converters and methods” by Ashburn et al., U.S. Pat. No. 6,362,608 and “Multi-phase and multi-module power supplies with balanced current between phases and modules” by Yang et al., U.S. Pat. No. 6,404,175. However, one problem of these prior arts is the limited parallel channels. Typically, mere two or three channels are developed in terms of the disclosures of the prior art. The limited parallel channels cause inflexibility of the application of the parallel-output technologies, especially for off-line power supplies. Another disadvantage is the balance current approach that requires the measurement of the switching current. The switching current measurement normally causes power losses.